The objectives of this program include development of cell culture systems for in vitro carcinogenesis studies and an assessment of changes in the microenvironment which lead to injury or death. Exposure of cultures or medium to low intensity fluorescent light is associated with hydrogen peroxide production and chromosome damage. Other studies show that use of a lowered oxygen concentration for growth of epithelial cells does not promote proliferation, as might be anticipated from studies with fibroblast-like cells; use of greater than atmospheric oxygen concentrations is not markedly beneficial.